Magnesium base alloy



Patented ov. 7,193

auasn ATENT OFFi MAGNESIUM BASE ALLOY John A. Gann, Midland, Mich,assignor to The Dow Chemical Company, Midland, Mich, a corporation ofMichigan 2 Claims.

The present invention relates to magnesium alloys and particularly tothose in which magnesium predominates.

Binary alloys of magnesium and copper have 5 been known for a long time,but they have not been used commercially because of their relatively lowmechanical properties and their poor corrosion resistance.

The primary object of this invention is to produce magnesium alloyscontaining copper, having improved mechanical properties and corrosionresistance. Another object is to produce magnesium alloys containingcopper that are amenable to heat treatment. Other objects and ad- 5vantages Will appear as the description proceeds.

The invention is based on the discovery that the properties andcharacteristics of the binary magnesium-copper alloys can be enhancedvery materially by the addition of definite amounts of lead and thatthese ternary magnesium-copperlead alloys can be further improved by theaddition of definite amounts of at least one of the low-melting metalstin and zinc.

I have discovered that beneficial effects due to the addition'of lead tothe binary magnesiumcopper alloys are obtained in general in alloyscontaining from about 0.5 to 15 per cent of copper to Which has beenadded from about 0.5 to 20 per cent of lead. The amount of improvementdepends on the relative percentages of copper and lead and on thecondition of the alloy, whether cast, heat treated, or wrought. I'havealso dis- 5 covered that additional improvements in properties and incorrosion resistance can be obtained by adding certain percentages oftin and/or zinc to these ternary magnesium-copper-lead alloys. Suchquaternaryand quinary magnesium alloys may contain from about'0.5 to 15per cent of copper, from about 0.5 to 20 per cent of lead, from about0.5 to 10 per cent of tin, and from about 0.5 to 10 per cent of zinc.For' many purposes I gprefer to use an alloy containing 80 per cent ormore of magnesium and 20 per cent or less of total added metals.

The following examples serve to illustrate the 7 property improvementsobtainable in these magnesium-copper-lead alloys. A casting alloycontaining 2 per cent of copper had the following properties:

Tensile strength lb./sq.in 12,200

Yield strength lb./sq. in- 5,100 Elongation per cent 3 The addition oflead in amounts varying from 3 to 8 per cent gave all ys with thefollowing improved properties:

Tensile strength lb./sq.in 13,500-16,700 6 Yield strength lb./sq.in5,300-5,900 Elongation per cent 3.0-4.7

Similar property improvements-were likewise obtained in the higherpercentage copper alloys.

For example, a binary magnesium-copper alloy 10 containing 6 per cent ofcopper had the following properties:

The addition of 2 to 6 per cent of lead gave the following improvedproperties:

Tensile strengthlb./sq. in 20,500-21,200 Yield strength lb./sq.in9,500-9,800 20 Elongation per cent 3.5-4.5

The additional property improvements obtained by, adding at least one ofthe low melting metals, tin and zinc, to the above described ternarymagnesium-copper-lead alloys are exemplified by the followingillustrations. A ternary magnesium alloy containing 2 per cent of copperand 8 per cent of lead had a yield strength of 5,900 pounds per squareinch and a Brinell hardness of 37.0. The addition of 2 and 4 per cent oftin raised these values to 6,400 and 7,200 pounds per square inchrespectively and to 38.1 and 42.2 Brinell hardness respectively. Anotherternary magnesium alloy containing 6 per cent of copper and 6 per centof lead had a yield strength of 9,800 pounds per square inch and aBrinell hardness of 41.1. The addition of 3, 5, and 8 per cent of tinraised these values -to 10,400, 12,600, and 13,000 pounds per squareinch respectively, and to 42.8, 46.9, and 48.4 Brinell hardnessrespectively. In another instance, a quaternary magnesium alloycontaining 2 per cent of copper, 8 per cent of lead, and 4 per cent oftin had a yield strength of 7,200 pounds per square inch and a Brinellhardness of 42.2. The addition of 2, 4, and 8 per cent of zinc raisedthese properties to 8,700, 9,200, and 11,300 pounds per square inchrespectively, and to 44.3, 45.6, and 48.9 Brinell hardness respectively.Again, the ternary magnesium alloy containing 60 2 per cent of copperand 2 per cent of lead had a tensile strength of 12,400 pounds persquare inch,

2. yield strength of 5,200 pounds per square inch, and a Brinellhardness of 35.9. The addition of 8 per cent of zinc raised theseproperties to 22,600

pounds per square inch, 8,600 pounds/per square inch, and a Brinellhardness of 44.3 respectively.

Similar property improvements were likewise obtained in alloyscontaining higher percentages of 5 copper and/ or lead.

Many of the specific alloy compositions falling within the scope of thisinvention are amenable to heat treatment. A solution heat treatment (S.H. T.) consisting of 16 hours'at 425-450 C.,

for example, produced a marked increase in the" percentage elongationand impact toughness of most of the alloys. Improvements amounting to20-300 per cent were obtained, the amount of property improvementdepending on the composition of the alloy. This treatment likewiseresulted in a 10 to 30 per cent improvement in the tensile strength ofsome of the alloys, particularlyv those containing appreciable amountsof zinc; and a subsequent precipitation heat treatment or aging (S. P.H.'T.) for 16 hours at 175 C. resulted in still further propertyimprovement, particularly in yield strength and hardness. This can beillustrated by the following examples:

Mg+2Cu+4Pb +8Zn-- Property S H T E Ten ile strength 21, 200 28, 400 l28, 200 Yield strength 8, 500 8, 100 16, 100 Elongation... per cent 4.28.3 3.0 Impact toughness it.- 2. 9 8. 9 4. 3 44. 3 44. 0 56.5

Brincll hardness e Sand 8. P Property cast S. H. T 1LT Tensile strength;lb. 'sq. 111.. 19, 900 20, 600 '30, 300 Yield strength "0 lb./sq. in11,300 10,300 21, 600 1. 9 5. 5 l. 6 1. 3 5. 6 2. 2 4s. 9 49. 4 66.8

I have likewise discovered that the corrosion resistance of themagnesium-copper alloys may be markedly improved by the addition of leadand that the corrosion resistance of these ternarymagnesium-cop-per-lead alloys may be still further improvedby theaddition of at least one of the metals, tin and zinc. Intheseinvestigations,

nate immersion treatment in a 3 per cent solution of common salt (NaCl).The samples were'in the salt solution approximately 15 seconds and thenwithdrawn and exposed to the air for approximately 2 minutes. This cyclewas repeated continuously throughout the entire test. The'loss in weightwas measured at.the end of definite time intervals, usually 24 hours,and the results expressed as a decrease in the corrosion rate. Theaddition of lead, for example, in amounts varying from 2 to 8 per centresulted in a 55 to 70 per cent reduction in the corrosion rate of thebinary magnesium alloy containing 2 per cent of copperi In anotherinstance the addition of 6 per cent of lead the magnesium alloycontaining 6 per cent of copper reduced the corrosion rate of the heattreated alloy by 68 per cent. It should be noted that heat treatmentimproved the corrosion resistance of the binary magnesium-copper alloys,but that this effect appears to be carried over to themagnesium-coppef-lead a1- loys where it is augmented by thebeneficialeffect due to the presence of lead.

(J It has likewise been discovered that the corroduction of castings.

the alloy specimens were subjected to an altersion resistance of the newternary magnesiumcopper-lead alloys can be further improved by theaddition of small amounts of at least one of the'low melting metals, tinand zinc. For example, the addition of 2 per cent of tin to a magnesiumalloy containing 2 per cent of copper and 8 per cent of lead reduced thecorrosion rate by about 47 per cent, or about-83 per cent'as compared tothe original magnesium alloy containing 2 per cent of copper. Theaddition of 3 per cent of tin to a magnesium 'alloy containing 6 percent of copper and 6 percent of lead was found to reduce the corrosionrate approximately 50 per cent, or about 84 per cent as compared to theoriginal magnesium-copper alloy. Likewise; the addition of Sper cent ofnine to a magnesium alloy containing 2 per cent of copper, 8 per cent"of lead, and 4 per cent of tin reduced the corrosion rate by 84 percent, or 98 per cent as compared with the original magnesium alloycontaining 2 'per cent of copper. Again, the addition of 8 per cent ofzinc to a magnesium alloy containing 2 per cent of copper and 2 per centof lead reduced the corrosion rate by about 98 per cent or about 99 percent as compared with the original magnesium alloy containing 2 per centof copper. Solution and precipitation heat treatments have likewise beenfound beneficial in the case of these quaternary and quinary alloys.

The use for which the alloy is intended is an important factor inestablishing its composition. Alloys with relatively high percentages ofcopper and relatively low percentages of lead, 'or of lead plus at leastone of the metals tin and zinc, are best where high thermal propertiesare required. On the other hand, if corrosion resistance and propertiesobtainable by heat treatment are more important the alioys should, ingeneral, contain a smaller percentage of copper than of lead, tin, andzinc. Alloys *containing 2 to 10 per cent of copper and 2 to 10 per centof lead; or 2 to 8 per cent of copperyZ to 8 per cent of lead, and 2 to8 per cent each of at least one'of the metals tin and zinc are ingeneral suitable for the pro- For extruded shapes, the alloy shouldpreferably contain less than 12 per cent ,total added metal.

The above'alloys may be prepared by the well known methods of meltingmagnesium with a protective flux and adding thereto the respectivealloying ingredients, either singly or simultaneously. Castproduct'stherefrom are made in dies or in sand containing an oxidation inhibitor,such as ammonium fluoride compounds. Heat treatment of themagnesium-copper alloys containing leadand lead plus tin may beconducted at 450 C. for approximately 15 to 30 hours, while thezinc-bearing show should be heat treated fer the same time atapproximately 425 C. Aging or precipitation heat treatment may beconducted for 18 to 24 hours at to C. Extruded shapes are produced bydie extrusion at temperatures of 250 to 400 C.

This application is a division of my co-pending application Serial No.120,426 filed January 13, 1937. I

Other modes of applying the principle of my invention may be employedinstead of those-explained, change being made as regards the in- -to 15per cent of copper, from about 0.5 per cent to 20 per cent of lead, fromabout 0.5 per cent to 10 per cent of tin, and from about 0.5 per cent to10 per cent of zinc, the balance being mag- 5 nesium.

2. An alloy containing from about 2 per cent to 8 per cent of copper,from about 2 per cent to 8 per cent of lead, from about 2 per cent to 8per cent of tin, and from about 2 per cent to 8 pe cent of zinc, thebalance being magnesium.

JOHN A. GANN.

